1. Field of the Invention
The present invention relates to a technique for improving the impact resistance of a rotating device, in particular, of a thin structure rotating device.
2. Description of the Related Art
Rotating devices, such as hard disk drives (hereinafter, sometimes referred to as disk drive devices, or HDDs), have been mounted in various electronic apparatuses by the size and weight thereof being reduced while the capacity thereof has been increased. In particular, rotating devices have been mounted in mobile electronic apparatuses. Although there is a demand that the rotating device to be mounted in such the mobile electronic apparatus should have improved impact resistance to withstand an impact occurring when dropped, etc., there is the possibility that the impact resistance may be decreased when the size, thickness and weight thereof are reduced, as stated above. That is, there is the trade-off demand that the rotating device to be mounted in a mobile electronic apparatus should have an improved impact resistance while it should be reduced in size and weight. The rotating devices to be required as described above include a disk drive device in which a fluid dynamic bearing unit (hereinafter, sometimes referred to as a FDB) is mounted. For example, the FDB mounted in the disk drive device disclosed in Japanese Patent Application Publication No. 2010-175046 is composed of a fixed body and a rotating body, and lubricant is interposed between the two.
In a typical disk drive device having such an FDB, the FDB is attached to a base plate. And, a hub is rotatably supported with respect to the base plate via the FDB. A magnetic recording disk is mounted on the hub. The hub is joined to the outer circumferential surface of a shaft. The FDB comprises a sleeve housed in a housing, and part of the shaft is housed in the sleeve. A radial dynamic bearing is formed between the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft, so that the shaft to which the hub is joined is supported rotatably in the radial direction. A flange portion, which extends and protrudes radially outward, is formed at an end portion of the sleeve near to the hub. A thrust dynamic bearing is formed between the hub and the sleeve in the axial direction, so that the shaft to which the hub is joined is supported rotatably in the thrust direction. That is, the hub is supported rotatably with respect to the base plate via the FDB.
When the axial size of the disk drive device (rotating device) including the aforementioned FDB is to be made small, it is common that the axial dimension of the hub is also configured to be small. As a result, the axial dimension of the joint portion between the hub and the shaft becomes small. When an acceleration due to an impact is applied to the rotating device thus configured, a stress, the magnitude of which corresponds to a value obtained by multiplying the total mass of the magnetic recording disk and the hub by the acceleration due to the impact, is applied to and around the joint portion between the hub and the shaft. Accordingly, in order to maintain the impact resistance of the rotating device as before, a structure that can withstand the stress concentrated on and around the joint portion between the hub and the shaft must be adopted. That is, it has been needed to make the joint area between the hub and the shaft to be large by making the thickness of the whole hub to be large to the degree in which the hub can withstand the stress. In the current situation, however, the thickness of the hub becomes a bottleneck in making the thickness of the aforementioned rotating device to be small.